The major objective for this study is to investigate the mechanisms by which mammalian sperm are capacitated in vivo. The pig is the primary experimental animal. Attention is being directed toward characterization of the lipids and proteins of whole sperm and the plasma membrane of sperm before and after exposure to the secretions of the seminal vesicles, as well as detecting the alterations of these components during exposure of sperm to the secretions of the female reproductive tract. Both in utero and in vitro studies are being conducted. Lipids under investigation include phospholipids, neutral lipids (glyceride fatty acids, sterols), glycolipids and gangliosides. Proteins (including glycoproteins) are being studied by SDS-PAGE, immunoelectrophoresis and isoelectric focusing as well as by column chromatographic methods. Proteins exposed on the sperm surface are identified by lactoperoxidase-catalyzed iodination. Iodinated proteins from seminal plasma are used to study the interaction of seminal plasma proteins with sperm from vesiculectomized boars.